JB_submit5
Assignement 5
Josef Buršík
1. Because CaCO3 was proved to be present in the sample, I used the PDF entry 5-586 and compared the pattern of the unknown sample with those of the full pattern for CaCO3 in the PDF database. At the same time I marked all reflections showing remarkable large FWHM, where overlap with another phase could be observed. The result (in the column 5-586) I obtained was:
 
d (A)
I (%)
FWHM(°)
 5-586(d, Irel)
 note
4.27
28 
0.27
- 
 
3.86
12 
0.30
 3.86, 12
 
3.343
82 
0.25
 -
 
3.035
100 
0.28
3.035, 100 
 
2.845
3 
0.28
2.845, 3 
 
2.742
12 
0.35
- 
overlap ? 
2.503
2 
0.36
 -
 overlap ?
2.495
15 
0.28
 2.495, 14
 
2.458
10 
0.22
 -
 
2.284
29 
0.43
 2.285, 18
overlap ? 
2.237
4
0.23
-
  
2.128
8
0.23
-
  
2.102
6
0.35
-
overlap ?
2.095
18
0.27
2.095, 18
  
1.98
4
0.23
-
  
1.939
2
0.37
-
overlap ?
1.927
5
0.29
1.927, 5
  
1.913
17
0.28
1.913, 17
  
1.875
17
0.28
1.875, 17
  
1.817
15
0.22
-
  
1.7
5
0.35
-
  
1.672
6
0.23
-
  
1.659
2
0.24
-
  
1.626
4
0.29
1.626, 4
  
1.604
8
0.28
1.604, 8
  
1.587
2
0.29
1.587, 2
  
1.541
12
0.23
-
  
1.525
5
0.28
1.525, 5
  
1.518
4
0.3
1.518, 4
  
1.51
4
0.42
1.51, 3
overlap ?

All stronger reflections of 5-586 entry was found in the unknown sample with good agreement on both relative intensities, and the dhkl spacings. This indicates that the CaCO3 is present in the sample as a structural pure phase (isotropic, without large lattice distortion). (At least) two reflections (2.284 and 1.51 d-spacings) exhibit larger values of FWHM. This might indicate an overlap of CaCO3 reflections with that of a second/third phase.
 

2. I supposed that both remaining phases exhibit neither texture, nor prefered orientation. With this assumption the two remaining strongest reflections (d1 = 4.27, and d2 = 3.343) should be also the strongest reflections of second/third phases. Starting with the reflection d2 = 3.343 I search through the given range of entries in the Hanawalt manual trying to find the phase which exhibits the strongest reflection at the same d-spacing, and at the same time the rest of its reflections do not contradict to the list of reflections of the unknown sample. To find the second phase was relatively easy even using only the Hanawalt search entries, because there was very good agreement between reflections in the unknown sample and 8 reflections given for the entry No. 5 - 490 (SiO2). The comparison between the rest of unknown reflections and the full list of reflections of 5 - 490 entry, which I obtained after the submision, is given the column 5 - 490.
 

d (A)
I (%)
FWHM(°)
 5-586(d, Irel)
 note
5-490(d, Irel)
4.27
28 
0.27
- 
 
4.26, 35
3.86
12 
0.30
 3.86, 12
 
  
3.343
82 
0.25
 -
 
3.343, 100
3.035
100 
0.28
3.035, 100 
 
  
2.845
3 
0.28
2.845, 3 
 
  
2.742
12 
0.35
- 
overlap ?
  
2.503
2 
0.36
 -
 overlap ?
  
2.495
15 
0.28
 2.495, 14
 
  
2.458
10 
0.22
 -
 
2.458, 12
2.284
29 
0.43
 2.285, 18
overlap ? 
2.282, 12
2.237
4
0.23
-
 
2.237, 6
2.128
8
0.23
-
 
2.128, 9
2.102
6
0.35
-
overlap ?
  
2.095
18
0.27
2.095, 18
 
  
1.98
4
0.23
-
 
1.98, 6
1.939
2
0.37
-
overlap ?
  
1.927
5
0.29
1.927, 5
 
  
1.913
17
0.28
1.913, 17
 
  
1.875
17
0.28
1.875, 17
 
  
1.817
15
0.22
-
 
1.817, 17
1.7
5
0.35
-
 
  
1.672
6
0.23
-
 
1.672, 7
1.659
2
0.24
-
 
1.659, 3
1.626
4
0.29
1.626, 4
 
  
1.604
8
0.28
1.604, 8
 
  
1.587
2
0.29
1.587, 2
 
  
1.541
12
0.23
-
 
1.541, 15
1.525
5
0.28
1.525, 5
 
  
1.518
4
0.3
1.518, 4
 
  
1.51
4
0.42
1.51, 3
overlap ?
  

The agreement between reflections on unknown sample and the entry 5 - 490 is fairly good. This means that the phase alpha-SiO2 is present in the sample as a second phasein an ammount comparable to CaCO3 (82 vs. 100% relative intensity). The larger value of FWHM (and larger value of relative I - 29% - equals approx. to I(CaCO3) + I(alpha-SiO2)) for d-spacing 2.284 can be explained by the overlap of reflections alpha-SiO2 and CaCO3 , respectively.
 

3. From the remaining reflections the highest intensity shows the reflection at d = 2.742 A. Using the second series of the Hanawalt manual (for proper d-spacing) I tried to find compound, which three strongest reflections would match the remaining unknown reflections in the sample, and at the same time do not contradict the findings made previously. In case of doubt it helped me that according to the analysis the third phase should contain magnesium. I found the best match with the entry 8-479 for MgCO3. The result I summarised in the table:
 

d (A)
I (%)
FWHM(°)
 5-586(d, Irel)
 note
5-490 (d, Irel)
8-479 (d, Irel)
4.27
28 
0.27
- 
 
4.26, 35
  
3.86
12 
0.30
 3.86, 12
 
    
3.343
82 
0.25
 -
 
3.343, 100
  
3.035
100 
0.28
3.035, 100 
 
    
2.845
3 
0.28
2.845, 3 
 
    
2.742
12 
0.35
- 
overlap ?
  
2.742, 100
2.503
2 
0.36
 -
 overlap ?
  
2.503, 18
2.495
15 
0.28
 2.495, 14
 
    
2.458
10 
0.22
 -
 
2.458, 12
  
2.284
29 
0.43
 2.285, 18
overlap ? 
2.282, 12
  
2.237
4
0.23
-
 
2.237, 6
  
2.128
8
0.23
-
 
2.128, 9
  
2.102
6
0.35
-
overlap ?
  
2.102, 45
2.095
18
0.27
2.095, 18
 
    
1.98
4
0.23
-
 
1.98, 6
  
1.939
2
0.37
-
overlap ?
  
1.939, 12
1.927
5
0.29
1.927, 5
 
    
1.913
17
0.28
1.913, 17
 
    
1.875
17
0.28
1.875, 17
 
    
1.817
15
0.22
-
 
1.817, 17
  
1.7
5
0.35
-
 
  
1.7, 35
1.672
6
0.23
-
 
1.672, 7
  
1.659
2
0.24
-
 
1.659, 3
  
1.626
4
0.29
1.626, 4
 
    
1.604
8
0.28
1.604, 8
 
    
1.587
2
0.29
1.587, 2
 
    
1.541
12
0.23
-
 
1.541, 15
  
1.525
5
0.28
1.525, 5
 
    
1.518
4
0.3
1.518, 4
 
    
1.51
4
0.42
1.51, 3
overlap ?
  
1.51, 4

I would say that the third phase is present in a small ammount, only as an impurity (I1 reaches only 12 %). The large value of FWHM of this phase indicates that its structure is somehow distorted (lower crystalinity, small particles, or microstress).